My invention is an improvement for repeating fire weapons such as automatic pistols or machine guns. In such weapons a rapid cycle recurs wherein a round of ammunition feeds into the gun's chamber, is fired, and a spent ammunition casing is ejected from the chamber. The cycle typically occurs at 600 rounds per minute, although faster rates are common. The gun bolt, which closes the aft end of the chamber during firing, retracts away from the chamber after firing to permit ejection of the spent casing and feeding of a new round into the chamber. In some guns the bolt opens the chamber too quickly after firing, causing premature blow-back wherein high pressure gas from the fired round's propellant shoots too forcefully from the chamber and endangers a person holding the gun. This problem has previously been addressed by mechanisms which slightly delay retraction of the bolt from the chamber so that pressure in the chamber somewhat dissipates through the gun barrel before bolt retraction. Examples of these mechanisms are found on the German Sturmgewehr machine gun and the Heckler & Koch P7 pistol shown respectively at pages 514 and 463 in Small Arms of the World (12th ed., U.S. pub 1983, Stackpole Books).